An apparatus of this type is described in European Patent document no. EP 0 371 708.
However, this apparatus does not comprise a removable part. That which is understood to be a removable part is, for example, a power supply device formed by a set of accumulators. As these power supply devices are to be taken apart during the useful life of the apparatus, one does not wish them to have different aspects. They have even been sought to be more or less standardized, so that they can be adapted to the largest possible variety of apparatus.